This invention relates generally to traverse mechanisms of the type incorporating a diamond thread screw and a follower device associated therewith, wherein the follower and screw are intended to undergo reciprocating movement with respect to one another, all with a predetermined sense of relative rotation between two parts.
In the past a number of different reversing nut constructions for a diamond thread screw have been proposed and produced. Some of these incorporated annular nut bodies carrying multiple roller elements having generally conical tip portions which were adapted to engage the walls of a square thread formation. U.S. Pat. No. 3,779,094 issued Dec. 18, 1973 to Berger A. La Barre, and having common ownership with the present application, discloses one particular arrangement which was found to operate quite well. In the patented device, one roller was fixed axially with respect to the nut body, and additional rollers carried on slide blocks in the body were capable of being shifted axially from engagement with the walls of one groove of the diamond thread screw to the walls of the oppositely-directed groove, in order to change the axial direction of travel of the nut.
Suitable abutment means were provided for effecting the shifting of the rollers, as particularly illustrated in FIG. 10 of the patent. In one modification shown in FIG. 11, another type of abutment (156) was employed to shift the rollers, this arrangement incoporating a turnably-driven nut which drove a reciprocatable piston through the intermediary of the diamond thread screw.
While the device described above operated in a generally satisfactory manner, the shifting of the rollers had to be accomplished at precisely positioned intervals along the length of the diamond thread screw. That is, a roller could only be shifted axially of the nut body at such time as it entered an intersection of the right and left-hand grooves. Otherwise, jamming and malfunction would result. It has been found that with improper positioning of the abutments, there was a tendency for the rollers to run into the V-shaped tips of the diamond thread, sometimes resulting in snapping off of the said tips. Such an occurrence, of course, rendered the equipment inoperative, and necessitated either a repair of the chipped-off section or a complete replacement of the diamond thread screw. Even where breakage of the thread did not occur, there existed a tendency for excessive wear to occur if the abutment was not positioned at precisely the exact point along the length of the screw, such that little or no interference would be encountered between the roller and the V-shaped tips at the intersections of the thread grooves.
Still other reversing devices have been devised, incorporating roller arrangements adapted to perform specialized functions. One such arrangement is illustrated in U.S. Pat. No. 4,008,625 issued Feb. 22, 1977 to Surinder M. Malhotra, and having common ownership with the present application. This patented device involved tandem-connected nuts including spring means acting between them, arranged to reciprocate along a conventional screw. The effect of the spring was to bias the nuts in opposite axial directions with respect to one another, such that the rollers carried by one nut would engage one wall of the groove in the screw, with the rollers of the other nut engaging the opposite wall of the groove, this construction having the effect of minimizing or eliminating backlash. Also, slight variations in the thread lead along the length of the screw tended to be averaged out, resulting in better tracking of the nut over spaced-apart areas of the screw thread.
Additional devices involving diamond thread devices are illustrated in U.S. Pat. No. 4,022,076 issued May 10, 1977 to Joseph R. Metz, and U.S. Pat. No. 4,031,765 issued June 28, 1977 to Joseph R. Metz, both of these patents having common ownership with the present application. In U.S. Pat. No. '765, there is disclosed a traverse mechanism incorporating a diamond thread screw and nut follower, the follower carrying a series of thread-engaging balls which were adapted to ride in either the left or right-hand grooves of the screw. In this patented device, one ball was fixed with respect to the nut, with two additional balls on opposite sides of the fixed ball being capable of shifting axially of the nut body so as to enable the nut to reverse its axial direction of travel with respect to the screw, without reversing the sense of rotation of the latter.
U.S. Pat. No. '076 discloses a somewhat similar arrangement, except there is incorporated in the nut separate carriers for a series of balls, with the carriers being spring-biased toward one another in order to reduce or eliminate backlash. Reversal in the direction of travel of the nut was accomplished at the ends of the screw, wherein curved reversing grooves effected axial shifting of the appropriate balls.
While the devices described in the immediately preceding two patents operated in a satisfactory manner for their intended purposes, it can be appreciated that in these constructions the length of the stroke of the nut was fixed. That is, the nut was confined to movement along the full length of the screw in one direction until such time as it arrived at the reversing groove at one end of the screw, thereafter shifting direction and traveling again the full length of the screw. Because the length of the stroke was not adjustable, in most cases a particular screw had to be tailored to the proper length and thread pitch in order to achieve the desired stroke. The necessity for making up the diamond thread screw as a special part for each individual application resulted in extra equipment and expense, and thus constituted a distinct drawback where it was desired to provide a device which was flexible and adaptable to a number of different types of installations.
Efforts have been made to provide a reversing device incorporating ball-type roller elements wherein the nut could be reversed at a series of points along the length of the screw. One such arrangement is disclosed in U.S. application Ser. No. 038,478 filed May 14, 1979, the inventor being Joseph R. Metz, and this application having common ownership with the present application. In the reversing nut construction described in this co-pending application, there was provided an external cylindrical housing carrying an abutment pin (110) that could engage a trip pin (82) arranged to shift a ball element (70) carried by the nut.
It can be appreciated that the positioning of the abutment pin was critical, the location being so chosen as to begin shifting of the associated ball element at the proper time, that is, at such time as the ball was at an intersection of the thread grooves. Clearly, with an incorrect positioning of an abutment pin, there would result an attempt by the associated trip pin to shift the ball (70) at such time as it was not at an intersection, this, of course, causing jamming of the device, and malfunctioning or failure. Moreover, the number of individual parts required was seen to be relatively large, and their proper adjustment was sometimes found to be difficult to attain.